1. Field of the Invention
The invention relates to a vegetation element for greening artificial level expanses, in particular rooftops of buildings.
2. The Prior Art
For the greening of artificial level expanses, in particular the rooftops of buildings, vegetation elements are required which enable the growth of vegetation.
To this effect it has been known to use mats or elements of rock wool which inter alia comprise a substrate, and which, after pre-cultivation, are available as ready-made green vegetation elements. In many cases however, due to the possible loss of minute fibres, the use of rock wool is not desirable for health reasons. Yet vegetation elements made of mineral stone wool do offer the advantage of meeting the requirements for fire safety according to DIN 4102, part 7, without any further measures.
The German patent DE 25 13 686 discloses a supporting slab for soil-less vegetative growth, said supporting slab being produced by mixing flakes of at least partly open-pore plastic foams with nutrients and a binder as well as optionally with fillers. The foam materials and nutrients, as well as optionally the fillers, are mixed, while in a separate process a special adhesive mixture is produced, said adhesive mixture being subsequently evenly mixed with the mixture of foam materials and nutrients and optionally of fillers. The entire mixture obtained in this way is dried in a suitable mould, optionally under pressure and/or by application of heat; thus a vegetation slab is formed which comprises mainly plastic material with additives. A similar vegetation slab is known from the German utility model 79 35 851.
While such vegetation slabs have largely proven to be successful, they do not however meet the requirements prescribed by DIN 4102 part 7. So far it has been particularly difficult, in the case of hitherto known vegetation slabs, to provide proof of resistance to fires caused by flying brands and to radiated heat. Thus, for example a directive issued by the Minister for Urban Development, Habitation and Transport of the Land of North Rhine-Westphalia (no. 54 of 15.9.1989) prescribes that in the case of rooftops with extensive greening, resistance to fires caused by flying brands and to radiated heat is deemed to be adequate only if there is a substrate layer at least 3 cm in thickness comprising no more than 20% by weight organic components.
Thus, so far vegetation-bearing elements comprising a higher percentage of organic substrate particles have so far met with certain prejudices concerning fire safety.
However, from the point of view of plant physiology, a percentage of organic substances exceeding 20% by weight may well be advantageous, for only these organic components are able, in particular by natural decomposition processes, to release the required nutrients to the plants.